- What holds solid sodium together?
Answer: B
Sodium is a metal. Metals are held together in a crystal lattice, which is a network of cations
surrounded by a “sea” of mobile electrons.
- What holds solid ICl together?
Answer: D
ICl is a polar molecule. Polar molecules have a net dipole — that is, a center of positive charge
separated from a center of negative charge. Adjacent polar molecules line up so that the nega-
tive end of the dipole on one molecule is as close as possible to the positive end of its neighbor.
Under these conditions, there is an electrostatic attraction between adjacent molecules. The key
word here is solid, because if the question just asked for the force holding ICl (the molecule)
together, the answer would be covalent bonding.
- What holds calcium chloride together?
Answer: C
The metallic cations (Ca2+) are electrostatically attracted to the nonmetallic anions (Cl–).
- Which of the following liquids has the highest vapor pressure at 25°C?
A. Carbon tetrachloride, CCl 4
B. Hydrogen peroxide, H 2 O 2
C. Water, H 2 O
D. Dichloromethane, CH 2 Cl 2
E. Trichloromethane, CHCl 3Answer: D
You can rule out choice B, hydrogen peroxide, and choice C, water, because the very strong
hydrogen bonds between their molecules lower the vapor pressure (the ease at which the liquid
evaporates). Although answer A, carbon tetrachloride, the only nonpolar molecule in the list,
has only dispersion forces present between molecules, choice D, dichloromethane, has the low-
est molecular weight and consequently the lowest amount of dispersion forces.
Part II: Specific Topics